Transparent β -quartz glass ceramic with low lithium content
阅读说明：本技术 具有低含量锂的透明β-石英玻璃陶瓷 (Transparent β -quartz glass ceramic with low lithium content ) 是由 M·J·M·孔德 T·奥格 P·勒于得 于 2018-06-06 设计创作，主要内容包括：本申请提供β-石英的透明玻璃陶瓷,其组成含有少量锂,至少部分由所述玻璃陶瓷构成的制品、所述玻璃陶瓷的玻璃前体,还提供了所述制品的制备方法。所述玻璃陶瓷具有如下组成,除了不可避免的痕量之外不含氧化砷和氧化锑,以氧化物的重量％计,含有：62％至68％SiO<Sub>2</Sub>；17％至21％Al<Sub>2</Sub>O<Sub>3</Sub>；1％至<2％Li<Sub>2</Sub>O；1％至4％MgO；1％至6％ZnO；0至4％BaO；0至4％SrO；0至1％CaO；1％至5％TiO<Sub>2</Sub>；0至2％ZrO2；0至1％Na<Sub>2</Sub>O；0至1％K<Sub>2</Sub>O；使得Na<Sub>2</Sub>O+K<Sub>2</Sub>O+BaO+SrO+CaO＜6％；任选地最高至2％的至少一种包括SnO<Sub>2</Sub>的澄清剂；以及任选地最高至2％的至少一种着色剂。(The present application provides β -quartz transparent glass-ceramics, the composition of which contains a small amount of lithium, articles at least partially composed of the glass-ceramics, glass precursors of the glass-ceramics, and methods for the production of the articles, the glass-ceramics having a composition which, apart from unavoidable traces, is free of arsenic oxide and antimony oxide and which contains, in% by weight of oxides, 62% to 68% of SiO 2 (ii) a 17% to 21% Al 2 O 3 (ii) a 1% to<2％Li 2 O; 1% to 4% MgO; 1% to 6% ZnO; 0 to 4% BaO; 0 to 4% SrO; 0 to 1% CaO; 1 percent ofTo 5% TiO 2 (ii) a 0 to 2% ZrO 2; 0 to 1% Na 2 O; 0 to 1% K 2 O; so that Na is present 2 O+K 2 O + BaO + SrO + CaO is less than 6 percent; optionally up to 2% of at least one comprises SnO 2 The clarifying agent of (1); and optionally up to 2% of at least one colorant.)
1. A transparent glass-ceramic containing β -quartz solid solution as its main crystalline phase, the composition of which is free of arsenic oxide and antimony oxide, expressed as% by weight of oxides, except for unavoidable traces, and which comprises:
62% to 68% SiO2；
17% to 21% Al2O3；
1% to<2％Li2O；
1 to 4% MgO;
1% to 6% ZnO;
0 to 4% BaO;
0 to 4% SrO;
0 to 1% CaO;
1 to 5% TiO2；
0% to 2% ZrO2；
0 to 1% Na2O；
0 to 1% K2O；
So that Na is present2O+K2O+BaO+SrO+CaO≤6％；
Optionally, up to 2% comprises SnO2At least one fining agent; and
optionally, up to 2% of at least one colorant.
2. Glass-ceramic according to claim 1, wherein the composition comprises 1 to 1.9%, advantageously 1.5 to 1.9% Li2O。
3. The glass-ceramic of claim 1 or 2, wherein the composition comprises 17.5% to 19% Al2O3。
4. The glass ceramic of any one of claims 1 to 3, wherein the composition comprises 1% to 3% MgO.
5. Glass-ceramic according to any of claims 1 to 4, wherein the composition comprises from 1% to 4% ZnO, advantageously from 3% to 4% ZnO.
6. The glass-ceramic according to any of claims 1 to 5, wherein the composition comprises ZrO2Advantageously from 0.5% to 2% ZrO2Most advantageously 1% to 2% ZrO2。
7. The glass-ceramic of any of claims 1 to 6, wherein the composition comprises 0.05% to 0.6% SnO2Most advantageously 0.15% to 0.4% SnO2。
8. The glass-ceramic of any one of claims 1 to 7, wherein composition comprises V2O5As the colorant, it is used alone or in combination with at least one other colorant selected from the group consisting of: CoO and Cr2O3And Fe2O3。
9. The glass-ceramic of any one of claims 1 to 8 having a coefficient of thermal expansion CTE25-300℃Falling within +/-25x 10-7K-1Within a range of advantageously +/-20x 10-7K-1Within the range of (1).
10. An article, in particular a cooktop, constructed at least in part from the glass-ceramic of any of claims 1 to 9.
11. An aluminosilicate glass which is a precursor of the glass-ceramic of any one of claims 1 to 9, having a composition which is capable of yielding a glass-ceramic of any one of claims 1 to 9.
12. The glass of claim 11 having a liquidus temperature less than 1400 ℃, a liquidus viscosity greater than 200 pa.s; and/or advantageously a viscosity of 30Pa.s (T) at less than 1640 deg.C30Pa.s<1640℃)。
13. A method of making the article of claim 10, comprising, in order:
melting a raw material charge capable of vitrification, and then fining the resulting molten glass;
cooling the resulting clarified molten glass while shaping it into the desired shape of the target article; and
applying a ceramifying heat treatment to the shaped glass;
the method is characterized in that the composition of the charge is such that the glass ceramic obtained has a composition according to any one of claims 1 to 7, by weight.
14. The method according to claim 13, wherein the raw material charge capable of vitrification is free of As except for unavoidable trace amounts2O3And Sb2O3Which contains SnO2As fining agent, advantageously 0.05% to 0.6% SnO2。
Glasses and glass-ceramics having various compositions with low levels of lithium have been described in the prior art. Thus:
for aluminosilicate glasses that do not contain lithium and contain high levels of zinc, it is known to obtain Glass-ceramics containing β -quartz solid solution as the main crystalline phase, however, such Glass-ceramics are not transparent (they are opaque), their precursor glasses have low viscosity at the liquidus temperature, and the heat treatment required to crystallize (ceramming) the precursor Glass to obtain the Glass-ceramic is tedious (see book "Glass-ceramic technology" second edition, W).
patent application US 2016/0174301 describes glasses with a low CTE value (CTE)20-300℃<30x10-7K-1) Which would be a suitable material for manufacturing induction hob tops. The glasses are free of alkaline substances in their composition. Therefore, they are rather difficult to melt: first, they have high viscosity at high temperatures; and second, they have high resistivity, requiring very high voltages to process them in an electrically heated oven. Such glasses may be coloured by oxides of transition elements, but the presence of such colorants in these glasses hinders their melting by absorbing infrared radiation;
patent application WO 2005/010574 discloses an optical device comprising a microlens. A portion of the device is made of crystallized glass and the disclosed composition is broad. Contemplated CTEs are those from-40 to 80 ℃. The teaching of said prior art document departs from the content of one of the present applications;
patent application WO 2015/166183 (corresponding to patent application FR 3020359) describes a partially crystallized glass sheet which is optionally transparent and preferably free of color, CTE20-300℃The value falls at 20x10-7K-1To 40x 10-7K-1Within the range of (1). This document does not contain any indication that it is possible to obtain a composition having both the indicated composition and less than 20x10-7K-1CTE of20-300℃Data of a value; this document also does not contain any data on the viscosity at high temperatures. The compositions disclosed are very broad; they may contain from 1% to 2%, advantageously from 1.2% to 1.8%, preferably up to 1.5% by weight of Li2O；
Patent US 9446982 describes a colored transparent glass-ceramic containing β -quartz solid solution as the main crystalline phase and having a lithium content (expressed as Li) of 2 to less than 3% by weight2O) (relating to controlled crystallization, at least 2 wt%). For the glass-ceramics described, and the technical problems involved in making them compatible with their decoration, it is desirable to obtain a CTEThe environmental temperature is-700 DEG CIs at a value of 10x10-7K-1To 25x10-7K-1Within the range of (1);
patent application US 2013/0085058 addresses the problem of glass fining, which is a precursor of glass-ceramics of the Lithium Aluminosilicate (LAS) type, and more particularly avoids reboiling of such glasses (the only properties set forth in the examples relating to suitable fining). The glasses do not have more than 10 parts per million (ppm) of sulfur (S) in their composition. Their composition (As-free)2O3And Sb2O3) May contain 1% to 6% Li2And O. It contains no coloring elements. The compositions exemplified do not have ZnO and mostly have a high content of Li2O (3.5 wt% and 4 wt%);
patent application EP 1170262 describes Lithium Aluminosilicate (LAS) types suitable for use as optical waveguide elementsA transparent glass-ceramic. The specified composition is broad; most of the example compositions have a high content of Li2O and Al2O3And a low content of SiO2(ii) a And
patent US 9018113 describes a coloured transparent glass-ceramic that can be used as a cooking top in connection with induction heating. Their composition has 1.5% to 4.2% Li2O; the exemplified compositions have a high content of Li2O(>2.9 wt%). No data are given about the high temperature viscosity of the precursor glass.
Under these circumstances, the inventors investigated the potential presence of transparent glass-ceramics whose composition has a low content of lithium (less than 2 wt.% Li)2O (see below)), and it is entirely suitable for use as a material for manufacturing a cooktop in the case of induction heating, more particularly in the case of induction heating with heating control using infrared sensors (as described above, the maximum temperature reached by the cooktop in operation is about 400 ℃ (typically for induction heating) and not more than 300 ℃ (for induction heating with infrared sensors)). Such glass-ceramics need to meet the following specifications:
at target use thicknesses (sheets are typically 1 millimeter (mm) to 8mm thick, more typically 2mm to 5mm thick, and often 4mm thick), are transparent (even though they are typically highly colored); the glass-ceramic is required to have an integrated transmittance TL (%) equal to or greater than 1% and a diffusion percentage of less than 2%. For example, a spectrophotometer with an integrating sphere may be used for transmittance measurement. Based on these measurements, the integrated transmission (TL (%)) and the percentage diffusion (%)) in the visible range (380 to 780nm) were calculated using the standard ASTM D1003-13 (under a 2 ° observer, D65 illuminant);
CTE falling within +/-25x 10-7K-1Within a range of (-25x 10)-7K-1≤CTE≤+25x 10-7K1) And preferably is +/-20x 10-7K-1Within a range of (-20x 10)-7K-1≤CTE≤+20x 10-7K-1) For using induction heater devices (more specifically, with infrared sensors)Associated induction heater apparatus) is acceptable (it is understood that the CTE is less than or equal to +25 x10-7K-1Advantageously less than or equal to +20 x10-7K-1According to the spirit specified above in relation to the prior art teachings), and
the precursor glass has advantageous properties despite the higher content of Li2The precursor glasses of the prior art glass-ceramics of O have the same advantageous properties, namely:
the precursor glass must have a low liquidus viscosity (<1400 ℃) and a liquidus high viscosity (greater than 200pa.s, in fact greater than 400pa.s, preferably greater than 500pa.s) to facilitate formation; and/or advantageously:
the precursor glass must have a low viscosity at high temperatures (T30Pa.s <1640 ℃) to aid in clarification.
In other aspects, it is highly advantageous that the precursor glass is capable of being converted to a glass-ceramic in a short length of time (<3 hours (h)), more preferably in a very short length of time (<1h), and/or that:
the viscosity has a resistivity of less than 50 ohm-centimeters (Ω -cm) at 30 pascal-seconds (pa.s) (preferably less than 20 Ω -cm). It will be appreciated by those skilled in the art that there is no particular difficulty in obtaining these last two properties that may be optionally desired for the precursor glass (in view of the glass-ceramic composition described below).
Of particular interest are also transparent glass-ceramics intended to have their composition free of As2O3And Sb2O3(except for unavoidable trace amounts).
The inventors have established that such glass-ceramics exist in a composition that is therefore almost free of lithium (less than 2 wt.% Li)2O) and satisfies the above-mentioned requirements. The glass-ceramic constitutes a first aspect of the present application. Characteristically, these glass-ceramics have a composition which is free of arsenic oxide and antimony oxide, except for unavoidable traces, and which, in% by weight of oxides, has:
62% to 68% SiO2；
17％To 21% Al2O3；
1% to<2％Li2O；
1 to 4% MgO;
1% to 6% ZnO;
0 to 4% BaO;
0 to 4% SrO;
0 to 1% CaO;
1 to 5% TiO2；
0% to 2% ZrO2；
0 to 1% Na2O；
0 to 1% K2O；
So that Na is present2O+K2O+BaO+SrO+CaO≤6％；
Optionally, up to 2% comprises SnO2At least one fining agent; and
optionally, up to 2% of at least one colorant.
With respect to the specified amounts of each component involved (or potentially involved) in the specific compositions described above, the following can be specified (the extremes of each of the specified ranges (above and below) are included within the stated ranges).
SiO2(62％-68％)：SiO2Must be suitable for obtaining a precursor glass of sufficient viscosity to limit the devitrification problem. SiO 22The content of (b) is limited to 68% because only SiO is contained2The larger the content of (b), the larger the high-temperature viscosity of the glass, and thus the more difficult the glass is to melt.
Al2O3(17% -21%): the presence of ZnO and MgO in (relatively large) specific amounts allows control of Al2O3Is critical to limit the devitrification phenomenon. Excess Al2O3(>21%) makes the composition more likely to devitrify (into mullite crystals or other crystals) (see comparative example 15), which is undesirable. In contrast, Al2O3Too small an amount of (c) ((b))<17%) are detrimental to nucleation and formation of small β -quartz crystallites Al2O3A content of 17.5% to 19% (border included) is advantageous.
Li2O (1% to<2 percent of: the inventors have found that Li can be used in the reaction of Li2The content of O is limited to less than 2% (and thus said content is limited significantly) while obtaining a glass-ceramic satisfying the requirements specified above. The content is advantageously at most 1.9% (. ltoreq.1.9%). However, a minimum of 1% is necessary so that: a transparent material is obtained, maintaining a low high temperature viscosity, and maintaining satisfactory devitrification characteristics. This minimum amount is advantageously 1.5%. Thus, Li2O contents of 1.5% to 1.9% (border included) are most particularly preferred.
MgO (1% to 4%) and ZnO (1% to 6%): the inventors partially substituted Li by using these two elements in combination in a prescribed amount2O (present from 1% to less than 2%) achieves the desired results.
MgO, which reduces the high temperature viscosity, forms part of a β -quartz solid solution, has less effect on devitrification than ZnO (see below), but it greatly increases the CTE of the glass-ceramic (see comparative example 18), why its content should fall in the range of 1% to 4%, advantageously 1% to 3%.
ZnO this element also acts to reduce the high temperature viscosity of the glass and also forms part of the β -quartz solid solution, in contrast to Li2O which increases the CTE of the glass ceramic, but the increase is moderate, so that CTE values of less than 25x10 can be obtained-7K-1Or indeed less than 20x10-7K-1The glass-ceramic of (1). When present in too large an amount, it results in unacceptable devitrification. In a preferred manner, however, the content thereof is from 1% to 4%, very preferably from 3% to 4%.
TiO2(1% to 5%) and ZrO2(0 to 2%): ZrO (ZrO)2Are optionally present (but not mandatory). When present, it is typically present at a level of at least 0.1% for its effectiveness. In other words, ZrO2Is "absent" or effectively present, typically at a level of 0.1-2%. These elements (TiO)2And ZrO2) Enabling nucleation of the glass and enabling formation of a transparent glass-ceramic.The presence of a combination of these two elements makes it possible to optimize the nucleation. Too high TiO content2The content makes it difficult to obtain a transparent glass-ceramic. Advantageously, TiO2The amount present ranges from 2 to 4%. Too high ZrO2The levels resulted in unacceptable devitrification. Advantageously, ZrO2Is present in a content of 0.5% to 2%, very advantageously in a content of 1% to 2%.
BaO (0% to 4%), SrO (0 to 4%), CaO (0 to 1%), Na2O (0 to 1%) and K2O (0 to 1%): these elements are optionally present. To be effective, when present, each of the elements is typically present at a level of at least 100 ppm. In other words, the level of "absence" of BaO or effective presence of BaO is typically in the range of 0.01 to 4%; the "absence" of SrO or the level at which SrO is effectively present is typically in the range of 0.01 to 4% (but see below); the "absence" of CaO or the effective presence of CaO levels is typically in the range of 0.01 to 1%; "absence" of Na2O or Na2The level at which O is effectively present is typically in the range of 0.01 to 1%; and "absence" of K2O or K2The level at which O is effectively present is typically in the range of 0.01 to 1%. After crystallization, these elements remain in the remaining glass. They reduce the high-temperature viscosity of the glass and they contribute to ZrO2When ZrO dissolves2When present) and they have limitations for devitrification into mullite, but they also increase the CTE of the glass-ceramic. This is why the sum of these elements must be equal to or less than 6%. It can be observed that SrO is generally not present as an additional raw material because it is an expensive material. For this (SrO is not present as additional raw material), if SrO is present, it is present only in unavoidable traces (<100ppm) is present as an impurity contained in at least one of the used raw material or the used cullet.
A clarifying agent: the composition of the glass-ceramic advantageously comprises at least one fining agent, which comprises SnO2. When present, the at least one fining agent is present in an amount effective (for chemical fining) and typically no more than 2% by weight. Due to the fact thatThis is typically present in the range of 0.05 to 2 wt%.
In a particularly alternative manner, and for environmental reasons, in the glass-ceramic compositions of the present application, by using SnO2Clarification is obtained, typically in the range of 0.05 to 0.6 wt.% SnO2(specifically, 0.15 to 0.4% by weight), the glass-ceramic composition of the present application containing neither As2O3Does not contain Sb2O3Or only unavoidable traces of at least one of these toxic compounds (As)2O3+Sb2O3<1000 ppm). At least one of these compounds, if present in trace amounts, is a contaminant; this may be due, for example, to the presence of recycled materials of the cullet type (which originate from the old glass-ceramics that were refined with these compounds) in the feed of raw materials capable of vitrification. In such cases, at least one other fining agent (e.g., CeO) is not excluded2Chlorine and/or fluorine) are present together, but preferably SnO is present2As a single fining agent.
It should be observed that the absence of an effective amount of chemical clarifying agent (or indeed the absence of any chemical clarifying agent) is not completely excluded; thermal clarification may then be performed. However, such non-exclusive variations are not preferred in any way.
Colorant: the composition of the glass-ceramic advantageously comprises at least one colorant. It is mentioned above in the context of a cooktop that it is suitable to mask elements arranged underneath said cooktop. The at least one colorant is present in an effective amount (typically at least 0.01% by weight); typical levels of presence are levels of up to 2 wt%, or indeed up to 1 wt%. The at least one colorant is typically selected from oxides of transition elements (e.g., V)2O5、CoO、Cr2O3、Fe2O3(see below), NiO, etc.) and oxides of rare earth elements (e.g., Nd)2O3、Er2O3Etc.). Preferably, vanadium (V) oxide is used2O5) Because the vanadium oxide results in low absorption in the glass, which is advantageous for melting. During the ceramization treatment, the absorption it achieves (during which it is partially reduced) is generated. Will V2O5With other colorants (e.g. Cr)2O3CoO or Fe2O3(see below)) combinations are particularly advantageous as this enables adjustment of the transmittance. The inventors have observed that by lowering Li2O content, V required to obtain the same coloration2O5Is less, which is also advantageous for cost reasons (because V is2O5Is a rather expensive element). See the following requirements (configured for use with thicknesses, typically 1mm to 8mm, more typically 2mm to 5mm, and often 4 mm):
the integrated Transmission (TL) is less than 10%, preferably less than 4%;
while maintaining the following transmission:
+ at 625 nanometers (nm) (T625mm) is greater than 1%, so that light from a red-emitting LED located below the board (cooktop) for display purposes can be passed through;
+ in the range of 950 nanometers (nm) (T950mm) in the range of 50 to 75%, thereby enabling the use of infrared electronic touch control, which transmits and receives at said wavelengths,
the following combinations of colorants (in% by weight with respect to the total composition) were found to be particularly advantageous:
V2O5is 0.005% to 0.1%,
Fe2O3is 0.01 to 0.32 percent,
Cr2O3is 0 to 0.1% by weight,
the CoO is 0 to 0.1%.
For the colorant, Fe2O3Has a special status. It has an impact on color and it is in fact often present in lesser or more important amounts as an impurity (e.g., from the raw material). However, the addition of some Fe is not excluded2O3To adjust the color. Which is acceptably "large" in the composition of the glass-ceramics of the present applicationThe amount "present makes it possible to use less pure and therefore generally less expensive raw materials.
The above-mentioned components (SiO) relating to or potentially relating to the composition of the glass-ceramic of the present application2、Al2O3、Li2O、MgO、ZnO、TiO2、ZrO2、BaO、SrO、CaO、Na2O、K2O, fining agents (including SnO2) And colorants) may in fact represent 100% by weight of the composition of the glass-ceramic of the present application, but a priori conditions are such that the presence of at least one other compound is not totally excluded, provided that it is present in small amounts (typically less than or equal to 3% by weight) and does not have a significant effect on the properties of the glass-ceramic. In particular, the following compounds may be present (their total content is less than or equal to 3% by weight, each of them being present in a total content of less than or equal to 2% by weight): p2O5、B2O3、Nb2O5、Ta2O5、WO3And MoO3。
Thus, the above-mentioned components (SiO) relating to or potentially relating to the composition of the glass-ceramic of the present application2、Al2O3、Li2O、MgO、ZnO、TiO2、ZrO2、BaO、SrO、CaO、Na2O、K2O, fining agents (including SnO2) And colorants) occupy at least 97% by weight or indeed at least 98% by weight or indeed at least 99% by weight or even 100% by weight of the composition of the glass-ceramic of the present application (see above).
Thus, the glass-ceramics of the present application contain SiO2、Al2O3、Li2O, ZnO and MgO as essential constituents of β -quartz solid solution (see below.) this β -quartz solid solution represents the predominant crystalline phase this β -quartz solid solution typically occupies more than 80% by weight of the total crystalline proportion<2％)。
The glass-ceramics of the present application contain about 10 wt.% to about 40 wt.% residual glass.
In a second aspect, the present application provides an article at least partially comprised of the glass-ceramic of the present application described above. Optionally, the article consists entirely of the glass-ceramic of the present application. Advantageously, the article constitutes a cooktop, which is a-priori block-colored (see above). However, this is not the only application that can be used. In particular, they may also constitute the material (whether or not coloured) constituting the cooktop, microwave oven panel, oven door. It will of course be appreciated that the glass-ceramics of the present application are logically intended to be compatible with their CTE. Therefore, the use of induction heating devices, in particular associated with infrared sensors, is strongly recommended for the cooktop.
In a third aspect, the present application provides a lithium aluminosilicate glass as a precursor for the glass-ceramics of the present application, as described above. Characteristically, the glass has a composition such that it enables to obtain the glass-ceramic. The composition of the glass generally corresponds to that of the glass-ceramic, but need not correspond exactly, as long as the skilled person is fully aware that the heat treatment performed on such glass to obtain a glass-ceramic may slightly affect the composition of the material. The glasses of the present application are obtained in a conventional manner, so that the raw material charges capable of vitrification are melted (the raw materials constituting them are present in the appropriate proportions). It will be appreciated (and not to the surprise of the person skilled in the art) that the charge in question may contain cullet. Said glasses are of particular interest for the following reasons:
they have advantageous devitrification properties, in particular compatibility with forming processes involving rolling, float and pressing. The glass has a low liquidus viscosity (<1400 ℃) and a liquidus high viscosity (>200pa.s, in fact >400pa.s, preferably >500pa.s), and/or advantageously:
they have a low viscosity (T) at high temperatures30Pa.s<1640℃)。
In other aspects, it is noted that the glass-ceramics of the present application can be obtained (from the precursor glass) by performing short duration ceramming (crystallization) thermal cycles (less than 3h), preferably very short durations (less than 1h), and the resistivity of the precursor glass is low (at a viscosity of 30pa.s, resistivity less than 50 Ω. cm, preferably less than 20 Ω. cm).
Low liquidus temperatures, high viscosities at the liquidus and low viscosities at high temperatures (see above) are of particular importance.
In its final aspect, the present application provides a method of making an article comprised at least in part of the glass-ceramic of the present application, as described above.
The method is analogized.
In a conventional manner, the method comprises a heat treatment of a charge of raw vitrifiable material (it being understood that such charge may contain cullet (see above)), the conditions of the heat treatment ensuring continuous melting and fining, followed by a shaping of the fined molten precursor glass (which may be by rolling, pressing or floating), followed by a ceramization (or crystallization) heat treatment of the shaped fined molten precursor glass the ceramization heat treatment generally comprises two steps, a nucleation step, and a further step of causing crystal growth of β -quartz solid solution the nucleation is generally carried out at a temperature in the range 650 ℃ to 830 ℃ and the crystal growth is in the temperature range 850 ℃ to 950 ℃.
Thus, the method of making an article comprised at least in part of the glass-ceramic of the present application comprises, in order:
melting a raw material charge capable of vitrification, and then fining the resulting molten glass;
cooling the resulting clarified molten glass while shaping it into the desired shape of the target article; and
applying a ceramifying heat treatment to the shaped glass.
The two successive steps of obtaining a shaped, fined glass (precursor of a glass-ceramic) and ceramming the shaped, fined glass may be performed immediately after one another, or they may be spaced apart in time (at the same site or at different sites).
Characteristically, the composition of the raw material charge capable of vitrification makes it possible to obtain the glass-ceramic of the present application, having the composition (in weight) specified above (advantageously comprising SnO)2As a clarifying agent (in the absence of As)2O3And Sb2O3In the case of (c)), preferably as a single clarifying agent). It is entirely conventional to ceramify the glass obtained from such charges. As mentioned above, the ceramization can be obtained in a short length of time: (<3h) Or indeed within a very short length of time (<1h)。
In the context of the manufacture of an article (e.g., a cooktop), the precursor glass is cut after shaping and before being subjected to a ceramming process (ceramming cycle). It is also typically edge treated, rounded, shaped and decorated. Such shaping and decorating steps may be carried out before or after the ceramifying heat treatment. The decoration can be performed, for example, by screen printing.
The present application will be illustrated below by examples and comparative examples.
Examples
To produce 1 kilogram (kg) of precursor glass batch, the raw materials were carefully mixed in the proportions specified in the first part of the table below (proportions in terms of oxides (% by weight of oxides)) (the table is divided into pages).
The mixture was melted in a crucible made of platinum. The crucible containing the mixture was then introduced into an oven preheated to 1550 ℃. In which they are subjected to a melting cycle of the type:
the temperature is increased from 1550 ℃ to 1670 ℃ within 1 h;
the temperature was maintained at 1670 ℃ for 5 hours and 30 minutes.
The crucible was then removed from the oven and the molten glass was poured onto a preheated steel plate. It was rolled to a thickness of 6mm on a plate. Thereby obtaining a glass sheet. They were annealed at 650 ℃ for 1h and then slowly cooled.
The properties of the glass obtained are referred to in the second part of the table below.
The viscosity was measured with a rotational viscometer (Gero).
T300Pa.s(° c) corresponds to a temperature at which the glass viscosity is 30 pa.s.
The resistivity of the glass was measured at high temperature using a 4 point contact RLC bridge with molten glass having a thickness of 1 centimeter (cm). The table gives the resistivity measured at a temperature at which the viscosity is 30 pa.s.
TLiquidus line(° c) is the liquidus temperature. The liquidus is given as the following relative temperature and viscosity ranges: the highest temperature corresponds to the minimum temperature at which no crystals are observed and the lowest temperature corresponds to the maximum temperature at which crystals are observed.
The devitrification characteristic is determined as follows. 0.5 cubic centimeter (cm)3) The glass samples of (a) were subjected to the following heat treatment:
placing in an oven preheated to 1430 ℃;
maintained at this temperature for 30 minutes;
lowering to a test temperature T at a rate of 10 ℃/minute;
maintained at this temperature for 17 h; and
the sample was quenched.
The crystals that may be present were observed with an optical microscope.
The ceramization cycle was carried out as follows:
rapidly heating to 500 ℃ at most;
heating from 500 ℃ to 650 ℃ at a heating rate of 23 ℃/min;
heating from 650 ℃ to 820 ℃ at a heating rate of 6.7 ℃/min;
from 820 ℃ at a rate of 15 ℃/min to (specified in the table)Of) maximum temperature TMaximum value；
At this temperature TMaximum valueFor 7 minutes (all examples are ceramization 1 except example 18 (comparative example, see below));
cooling to 850 deg.C at 35 deg.C/min; and
cool to ambient temperature according to oven inertia.
For some examples (examples 1, 2, 4, 18 and 20), results were obtained at the end points of two different ceramization treatments (ceramization 1 and ceramization 2, which differ by their TMaximum valueThe numerical value of (c).